Photovoltaic or solar cells are semiconductor devices which can convert light to electricity. When the photovoltaic cells are exposed to light, they usually generate voltage via terminals formed therein to induce subsequent flow of electrons. The flow of electrons has a size proportional to light collision strength for photovoltaic cell junctions formed on the cell surface.
A representative kind of the currently known photovoltaic cells includes a silicon wafer-based photovoltaic cell and a thin film photovoltaic cell. The wafer is a semiconductor material prepared using a single crystal or multi-crystal ingot, and the like. In addition, a photovoltaic device in the thin film type photovoltaic cell is a continuous layer of a semiconductor material deposited on a substrate or a ferroelectric, and the like using a technique such as sputtering or chemical vapor deposition (CVD).
Both wafer-based photovoltaic cells and thin film type photovoltaic cells have brittleness, so that they require a load-tolerant supporting member configured to support the cells. The supporting member can be a top layer (for example, a ferroelectric layer) which is disposed on the upper part of the photovoltaic cells and has light permeability, or a rear layer disposed on the rear side of the photovoltaic cells. A photovoltaic cell module may include a top layer and a rear layer as described above simultaneously, and consist of rigid materials such as a glass plate; flexible materials such as a metal film or a metal sheet; or a suitable plastic material such as polyimide.
Here, the rear layer (for example, a substrate) has usually a rigid back-skin form for protecting the rear side of the photovoltaic cell module. Various materials which may be applied to such a substrate are known, an example of which includes ferroelectrics (for example, glass), organic fluoropolymers (for example, ethylene tetrafluoroethylene (ETFE), Tedlar or polyethyleneterephthalate (PET). Materials as described above may be applied to the module, alone or in a state coated with a silicon-based and/or oxygen-based material (for example, SiOx).
The photovoltaic cell module or solar cell module includes a single photovoltaic cell or an assembly of photovoltaic cells (photovoltaic cell array) electrically interconnected onto the ferroelectric and/or substrate. Such a photovoltaic cell or array is attached to the ferroelectric and/or substrate with an encapsulant to be capsulated. The encapsulant is used to form the integrated module by protecting the cells from external environments, encapsulating the cells and laminating the cells on the ferroelectric or substrate, and the like.
The most widely used encapsulant is an ethylene vinyl acetate (EVA)-based material which is used to attach photovoltaic cells or photovoltaic cell arrays to ferroelectrics and to be subjected to encapsulation. The encapsulant is usually provided in a film, and laminated on cells and ferroelectrics and/or substrates.
The currently known encapsulants for a photovoltaic cell module have the following problems. In encapsulants such as widely used EVA-based materials, adhesivity of glass and modules with the other members is degraded. Therefore, when a photovoltaic cell module is used for a long time, detachment is easily induced at each layer in the module, which causes loss of efficiency or corrosion of the module caused by water permeation. In addition, the currently known encapsulants have lowered resistance against ultraviolet (UV) rays, and the like, and thus, when the module is used for a long time, a problem such as bleaching or discoloration arises to lower efficiency of the module. Furthermore, the current encapsulants such as EVA-based materials cause stress upon hardening, thereby causing damage to the module.